| 摘要 |
PURPOSE:To prevent perfectly a digital circuit from malfunctioning when the electric power source is turned on or off, by keeping a transistor out off until the electric power voltage reaches a prescribed voltage. CONSTITUTION:Until electric power voltage VCC increases up to the sum of Zener voltage VZ across constant voltage diode D1, base-emitter voltage VBE of transistor TRQ1 and voltage drop VR2 across resistance R2, TRQ1 stays cut off, so that reset output V1' will be at logic 0. For this purpose, using this circuit as a resetting circuit permits the reset output to stay at 0. When voltage VCC further increases over VZ+ VBE+VR2, the base current of TRQ1 flows to diode D1 via resistance R2 to turn on TRQ1 and reset output V1' increases nearly following up the electric power voltage, thereby releasing the reset state. |
